1. Field of the Invention
The field relates to a device and a method for optical recording and a signal processing circuit,and more particularly, to a device and a method for optical recording and a signal processing circuit that are capable of optimizing a recording condition depending on the compatibility between a medium and a drive.
2. Description of the Related Technology
For recording onto an optical information recording medium such as CD-R or DVD-R (hereinafter referred to as “media” or a “medium”), the compatibility between a medium to be recorded on and a device to be used for recording (hereinafter referred to as a “drive”) depends on each combination of them. This may be caused by the medium side factor wherein the optimum recording condition is varied by the difference in a recording material comprising the medium or the film formation variation during production, or by the drive side factor wherein the optimum recording condition is varied by the difference in a pickup device and/or a semiconductor laser comprising the drive or assembly variation during production. In fact, a suitable recording condition exists for each combination of a medium and a drive due to the combination of those factors.
Accordingly, in a conventional method, ID information on a medium type identifiable by a drive is stored in the medium as well as a recording condition prepared for each medium type is stored in the drive. When recording is actually performed, the ID information stored in the medium is read from the medium loaded to the drive, and a recording condition related to the ID information is used.
However, in the conventional method, suitable recording conditions can be selected for pre-verified known media, but prepared recording conditions may not be adequate to accommodate unknown media that are not pre-verified. Further, depending on the change in the recording environment such as a recording speed, disturbance, or change over time, the prepared recording conditions may not be adequate even for known media.
A method contemplated to accommodate such an unknown medium is described in Japanese Unexamined Patent Publications No. 2003-30837 and No. 2004-110995
As described in the paragraph [0020] of the Japanese Unexamined Patent Publication No. 2003-30837 as “ . . . a phase error relative to a channel clock is detected for every recording pattern. A recording compensation parameter adjustment section 12 optimizes an emission waveform rule on the basis of the detection result at the phase error detection section 11,” a method of detecting a phase error by comparing with a channel clock and of correcting the phase error is disclosed.
Also, the paragraph [0024] of the document describes that “Next, a test pattern for determining an emission waveform rule is recorded. The area wherein the test pattern is recorded is reproduced, and the relationship between a prepared emission waveform rule and a phase error amount is examined. In other words, the phase error amount in the combination of the length of each mark and the length of each space immediately before the mark is measured. An emission waveform rule wherein the phase error amount becomes zero is estimated from the measured phase error amount, whereby a desired emission waveform rule is determined . . . ”, disclosing a method for measuring a phase error amount for every combination of a mark and a space, and then estimating an emission waveform rule wherein the phase error amount becomes zero (see FIG. 8 and FIG. 12).
The method disclosed in the Japanese Unexamined Patent Publication No. 2003-30837 is effective for optimizing a strategy because a correction is made based on a phase error of a recording pattern.
Also, the paragraph [0045] of the Japanese Unexamined Patent Publication No. 2004-110995 describes that “ . . . a top pulse corresponds to a 3T period and a non-multipulse corresponds to a 8T period are generated integrally (consecutively) . . . ” and the paragraph [0046] of the document describes that “ . . . the laser power for a write pulse is adjusted in two levels, and when the ratio between a laser power (a height value of the top pulse) Ph and a laser power (a height value of the non-multipulse) Pm is optimum, an optimum power can be obtained . . . ”, suggesting the effectiveness of optimizing the Ph/Pm ratio.
On the other hand, the adoption of PRML (Partial Response and Maximum Likelihood) method has been examined as a code identification scheme in a high-density recording system using a blue laser. The PRML method requires configuring a recording condition using a metrics different from that in a conventional slicing method in order to provide a high-quality recording because code identification in the method is performed on the basis of information on the amplitude of an RF signal obtained by reproducing a recording pattern.
With regard to methods for configuring a recording condition on the basis of information on the amplitude of an RF signal, the following patent documents are known: Japanese Unexamined Patent Publication No. 2004-13978, 2004-280876, 2003-15129, 2004-63024, 2004-213759, and 2004-152473.
Japanese Unexamined Patent Publication No. 2004-13978 and 2004-280876 disclose methods in which conditions for a top pulse, an intermediate pulse, and a last pulse are determined using an asymmetry as an indicator. Japanese Unexamined Patent Publication No. 2003-15129, 2004-63024, and 2004-213759 disclose methods for determining a recording pulse condition based on the difference between an ideal waveform on the assumption of PRML and a reproduced waveform obtained from an actual recording. Japanese Unexamined Patent Publication No. 2004-152473 discloses a method for determining a start position of a top pulse using an asymmetry as an indicator as well as widths of a top pulse and an intermediate pulse using a jitter as an indicator.
However, because the method disclosed in the Japanese Unexamined Patent Publication No. 2003-30837 involves, as conventional methods, a fine adjustment of a prepared strategy stored in a drive, it is difficult to provide favorable recording quality for media to which prepared strategies are not applicable.
Also, in the method disclosed in the Japanese Unexamined Patent Publication No. 2004-110995, as described in the paragraph [0067] of the document, the initial values of Ph and Pm are tentatively set based on values stored in a drive or a medium, and then the Ph/Pm ratio is calculated. Accordingly, as in the case of the Japanese Unexamined Patent Publication No. 2003-30837, it is difficult to provide favorable recording quality for media to which the tentatively set values are not applicable.
Furthermore, in the methods of Japanese Unexamined Patent Publication No. 2004-13978 and 2004-280876, because conditions for a top pulse and a last pulse are simultaneously determined using the same indicator, the shortest pulse that is most likely to cause an error is not optimized. Accordingly, the methods are amenable to disturbance and likely to cause an error, and therefore cannot easily provide a high-quality recording system with a large recording margin.
The methods disclosed in Japanese Unexamined Patent Publication No. 2003-15129, 2004-63024, and 2004-213759 also cannot easily provide a high-quality recording system with a large recording margin, similar to the methods in the Patent Documents 3 and 4, because a correction is made only for each of commonly known pulse shapes and therefore it is difficult to identify which part of a pulse shape is effective for which indicator.
The method disclosed in Japanese Unexamined Patent Publication No. 2004-152473 also cannot easily provide a high-quality recording system with a large recording margin, similar to the methods in the Patent Documents 3 and 4, because the widths of a top pulse and an intermediate pulse are simultaneously determined using a jitter as an indicator although a start position of the top pulse is determined using an asymmetry as an indicator.
It is therefore the object of the present invention to provide an optimization method of a recording condition depending on the compatibility between a medium and a drive, which is especially effective for the case where a code identification scheme is assumed, such as PRML in which code identification is performed on the basis of information on the amplitude of an RF signal.